Scavenger concentration, reducing radicals

The photoreactivity of the involved catalyst depends on many experimental factors such as the intensity of the absorbed light, electron-hole pair formation and recombination rates, charge transfer rate to chemical species, diffusion rate, adsorption and desorption rates of reagents and products, pH of the solution, photocatalyst and reactant concentrations, and partial pressure of oxygen [19,302,307], Most of these factors are strongly affected by the nature and structure of the catalyst, which is dependent on the preparation method. The presence of the impurities may also affect the photoreactivity. The presence of chloride was found to reduce the rate of oxidation by scavenging of oxidizing radicals [151,308] ... 

For treatment by the ZPU, a waste stream must be in the vapor phase at near-ambient pressure, at a temperature of less than 400°F, and relatively free of particulate matter. Each compound in the waste stream has unique requirements for destruction. Many compounds are destroyed with a low application of energy, while others require a stronger application. The dose required for a specific combination of contaminants must be determined experimentally. Moisture may either enhance or reduce system effectiveness depending on the mixture. Compounds that act as free-radical scavengers or reducing agents may diminish the process efficiency. Concentrations of vapors that produce temperatures above 400°F in the reaction chamber through exothermic reaction must be diluted to keep the temperature below 400°F. 

Low concentrations of radical scavengers can greatly reduce the density of crosslinking of liquid polymers although most radicals will be formed some distance from a scavenger. For a solid polymer much higher concentrations are needed, but crosslink densities can still be approximately halved. 

Matrix effects can be complex and difficult to predict because most co-solutes may compete with the reactant of interest for reactions with radicals, becoming effective scavengers that reduce the sonochemical efficiency. Taylor et al. [30] have observed a significant inhibition of the sonolysis of polycyclic aromatic hydrocarbons (PAHs) in the presence of dissolved organic matter. Substrate concentration effects on the rate constants have also been reported. When the target molecules are volatile, they partition between... 

There is competition for the free electrons between the positrons and the holes (OH radicals in the case of water media). When OH competes for these free electrons the addition of OH scavengers is predicted to cause an increase in the yield of o-Ps, a phenomenon called enhancement . On the other hand, addition of electron scavengers will reduce the yield of o-Ps, an effect known as inhibition . The yield of o-Ps is usually denoted by I3 (where and I2 are the yields of free positrons and />-Ps, respectively, having a much shorter half-life than o-Ps). Duplatre and coworkers - found that the yield of o-Ps in aqueous solution in the presence of concentration C of allylamine is given by equation 10. The enhancement factor 1 -h )SC is due to the reaction of allylamine with OH radicals, while the 1 + C inhibition factor is due to the reaction with aqueous or free electrons. The enhancement by amines is one of the main pieces of evidence for the existence of the spur mechanism . Yet, it should be emphasized that it does not rule out the simultaneous existence of both mechanisms . Duplatre and coworkers found that the inhibition by a strong inhibitor such as NO3 is the same in the presence or absence of allylamine. 

Generally, the total scavenger concentration is higher than that of reducing radicals. The reduction (reaction 6) therefore concerns only a portion of the silver cations atoms or clusters are generated in the presence of an excess of Ag" ions. The silver atoms formed through reaction 6 associate with excess silver cations at a diffusion-controlled rate (20). 

When stored for an appreciable length of time radioiodinated antibodies imdergo radiolysis leading to a loss in purity and immimoreactivity. The rate of radiolysis can be reduced by the addition of carrier proteins or antioxidants such as ascorbic add which scavenge the free radicals responsible (9). A concentration of 0.1-1% albumin or 0.5% ascorbic add is commonly used and... 

Membrane chemical degradation directly results from attack by active radicals. Hydrogen peroxide formed in fuel cells can result in radical formation. Some researchers add radical or HjOj scavengers to eliminate radicals or reduce the formed HjOj to harmless species. Aoki et al. (2006) confirmed that an appreciable fraction of HjOj or HO radicals was easily scavenged at Pt particles in the CL or in Pt-dispersed Nafion membranes. Danilczuk et al. (2009) found that Ce(III) in Nafion membranes with low concentrations can efficiently scavenge HO radicals because of the Ce(lll)/Ce(lV) couple redox... 

A comprehensive study of the chemical stability of polyacrylamide (PAA) polymers was conducted. The primary emphasis of the study was to determine the stability of Dow Pusher 500 PAA in Sundance brine at 115°F (46°C). Experiments were completed which show the effect of biocides, metals, ferrous and ferric iron salts, pH, surfactants, alcohols, antioxidants, sodium hydrosulfite, thiourea, plastic pipe, formaldehyde concentration, free radical scavengers, hydrazine, oxygen, and temperature on the chemical stability of PAA. Stability tests were conducted at temperatures ranging from room temperature to 221 F (105°C). The results showed that many substances caused substantial chemical degradation of PAA polymers in the presence of oxygen however, in many cases, the adverse effects of these substances could be reduced or eliminated by the proper selection of chemical stabilizers or the nearly complete removal of oxygen from the solutions. 

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